Signaling system



B. P. HAMILTON.

SIGNAUNGSYSTEM,

APPLICATION FILED FEB. 27, I919.

Patented Jan. 25,1921.

$ HH mm A TTORNEY UNITED STATES PATENT OFFICE.

BAXTER P. HAMILTON, OF BROOKLYN, NEXV YORK, ASSIGNOR T0 AMERICAN TELE- PHONE AND TELEGRAPHCOMPANY, A CORPORATION OF NEW YORK.

srenanrne SYSTEM.

Specification of Letters Patent.

Patented Jan. 25, 1921.

Application filed February 27, 1919. Serial No. 279,475.

T 0 all whom it may concern:

Be it known thatl, BAXTER P. I'TAMILTON, residing at Brooklyn, in the'county of Kings, and State of New York, have invented certain Improvements in Signaling Systems, of which the following'is a specification.

This invention relatesto signaling systems for transmitting simultaneously a plurality of signals by means of current impulses of different kinds, such, for instance, as direct current Morse impulses and alternating current impulses. It is especially applicable to such signaling circuits when composited with telephone lines, though not limited to this use. Its object is to improve the speed and quality of the signals in such systems by avoiding interference between the different currents employed in the sending and receiving apparatus.

The invention will be described in connection with the accompanying drawing showing diagrammatically one end of a system in which it is embodied.

The main line 1, is provided with the usual composite set 2 at'the point of connection between the telegraph leads 3 and the telephone lead 4, for the purpose of separating the telegraph and telephone currents. The telephone circuit is provided with the usual composite ringing apparatus 5 for signaling telephone subscribers. The telegraph lead 3 is provided with the usual duplex set 6 comprising ratio arms 7 .7 connected between the mainline 3 and the artificial lineS, with the sending relay 9- connected to their apex l0 and the receivingrelay 11 connected across their extremities at' the junction with the main and artificial lines.

For the purpose of providing an additional signaling channel, a second pair of ratio arms 12 and 12 are likewise con-: nected between the main and artificial lines,

and provided with a lead 13 connected to' their apex for the transmitting apparatus.

Where itis intended to use alternating current for signaling upon this additional channel, the receiving circuit may conveniently be connected to the ratio arms inductively by a transformer 1 1 having a primary winding'15 in each of the ratio arms. This transformer in turn feeds the receiving apparatus through a pair of transformers 16, 17 whose windings are loosely coupled, and through amplifiers 18 which may be of any desired type. The receiving apparatus here indicated is a polar relay 19 whose armature vibrates between contacts 20, both of which are connected in the circuit of the slow acting relay 21, the circuit being completed through the armature of the relay and the current source 22. Relay 21, when sufiiciently deenergize'd, closes the circuit of the lamp 23 to produce the signal. Alternating current close the circuit between the transformer and alternating current source to produce the signal impulses, and is preferably controlled by a relay 26 under the influence of a sending key 27 as shown. The source 24: preferablv generates a currentof a frequency different from the ringing frequency used on the telephone line and low enough to have little effect on telephone instruments, such, for instance, as fortys ive cycles. If the generated current is of sinusoidal form there will be little difficulty from interference; otherwise a filter circuit such as indicated at 28 may be necessary to prevent the higher harmonics from reaching the telephone circuit, and

causing disturbance. In any case it may be found well to use a filter since the sending key may be closed at any point of the generated voltage wave, and it closed at the top of the wave the. initial impulse may'have harmonics of a magnitude and frequency to reach the telephone.

If the main and artificial line are perfectly balanced for the frequency used,'the alternating current signals in the ratio arms 12 12 will present equal potentials in the opposite side of the direct current receiving relay 11 and hence cause no disturbance, but in practice, when the artificial line is adjusted to the desired balance for the ordinary Morse or direct current impulses, it is somewhat out of balance for alternating current signals of such frequencies as above mentioned, and there results a tendency to disturb the receiving relay 11. To prevent this a tuned shunt 29 is automatically con nected across the relay 11 whenever an alternating current signal is put upon the line.

As shown this includes inductance 30 and capacity 31 in the proper proportions for resonance with the alternating signaling current. The capacity being small, this shunt is substantially opaque to direct current signals intended for the relay 11. The shunt 29 may conveniently be arranged to close under the influence of the sending relay 26, as indicated at 32.

The unbalance of the circuit for the alternating current signals may also make it advisable to open the receiving circuit when alternating current signals are transmitted, and this also may be done by a contact under the influence of the sending relay 26, as indicated at 33.

Since the received alternating current signals are weak, it is advisable to reduce the impedance of the sending lead 13 for received signals in order that the maximum effect may be felt in the receiving transformer 15. To this end a back contact 341-. is provided for the sending switch 25, which serves to short circuit the primary of the sending transformer 23 when not in use.

It is found that the interference between the alternating current signals and the other signaling current is materially reduced by the introduction of condensers 35 35 into the ratio arms 12 12, and a condenser 36 in the circuit leading to the primary of transformer 16. The value of these capacities will depend upon the frequencies used. These in conjunction with the loosely coupled transformers 16 and 17 effect a very satisfactory separation of the direct current signals and the alternating current signals. and constitute a valuable reinforcement of the composite set 2 with respect to the alternating signaling impulses and the ringing current of the telephone circuit. If tight coupling transformers or ordinary repeating coils were used, the lower frequency impulses from the direct current signals would tend to pass through and operate the polar relay 19.

The particular circuit here shown and described is to be regarded as illustrative only, as it is obvious that various modifications may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. In a signaling system, a composite transmission circuit having channels for both telephonic and direct currentsignals, a duplex set for sending and receiving direct current signals over said circuit, a pair of ratio arms additional to those of said duplex set for providing a duplex channel for alter nating current signals, and a receiving circuit for the alternating current signals connected to said ratio arms by a loose coupling transformer.

2. In a signaling system, a composite transmission circuit having channels for both telephonic and direct current signals, a duplex set for sending and receiving direct current signals over said circuit, a pair of ratio arms additional to those of said duplex set for providing a duplex channel for alternating current signals, and a receiving circuit for the alternating current signals inductively related to said ratio arms, and condensers in the circuit on each side of said inductive connection for increasing the selectivity of said circuit for the alternating current signaling frequency.

3. In a signaling system, a composite transmission circuit having channels for both telephonic and direct current signals, a duplex set for sending and receiving direct current signals over said circuit, a pair of ratio arms additional to those of said duplex set for providing a duplex channel for alternating current signals, a receiving circuit for the alternating current signals inductively connected to said ratio arms, a loose coupling transformer in said receiving circuit, and condensers in the circuit on each side of said inductive connection for increasing the selectivity of said circuit for the alternating current signaling frequency.

4. In a signaling system, a composite transmission circuit having channels" for both telephonic and direct current signals, a duplex set for sending and receiving direct current signals over said circuit, a pair of ratio arms additional to those of said duplex set for providing a duplex channel for alternating current signals, and a shunt for the receiving branch of the direct current dnplex set containing impedance tuned to the frequency of the alternating signaling current and substantially opaque to direct current signals, and means for closing said shunt when alternating current signals are transmitted.

5. In a signaling system, a composite transmission circuit having channels for both telephonic and direct current signals, a duplex set for sending and receiving direct current signals over said circuit, a pair of ratio arms additional to those of said duplex set for providing a duplex channel for alternating current signals, a receiving circuit forv the alternating current signals inductively related to said ratio arms and containing a loose coupling transformer,-condensers in the circuit on each side of said inductive connection for increasing the selectivity of said circuit, a sending lead connected to said ratio arms and means for shunting the receiving branch of the direct current duplex set by a circuit opaque to the direct current signals buttuned to the alternating current signals when alternating cur rent signals are transmitted.

6. In a signaling system, a transmission line, a duplex set connected thereto for transmitting direct current signals, a pair of ratio arms additional to those of said duplex set for providing a duplex channel for alternating current signals, local sending and receiving circuits associated With said ratio arms, and means for connecting across the direct current receiving relay a shunt opaque to the direct current signals and tuned to the alternating current signals when alternating current signals are transmitted.

7. In a signaling system, a transmission line, a duplex set connected thereto for transmitting direct current signals, a pair of ratio arms additional to those of said duplex set for providing a duplex channel for alternating current signals, a receivingcircuit for the alternating current signals inductively related to sa1d ratio arms and condensers in the circuit of each' side of said inductive connection for increasing the selectivity of said circu1t for the alternating current signaling frequency.

8. In a signaling system, a transmission line, a duplex set connected thereto for transmitting. direct current signals, a pair of ratio arms additional to those of said duplex set for providing a duplex channel for alternating current signals, a receiving circuit for the alternating current signals inductively related to said ratio arms and containing a loose coupling transformer, condensers in the circuit on each side of said inductive connection for increasing the selectivity of said circuit to the alternating current frequency, and means Ior connecting across the direct current receiving relay a shunt opaque to the direct current signals and tuned to the alternating current signals, When alternating current signals are trans mitted.

In testimony whereof, I have signed my name to this specification this th day of February, 1919.

BAXTER P. HAMILTON. 

